1. Field of the Invention
The present invention relates to a method and apparatus for estimating a road traffic condition, and a method and apparatus for controlling a running characteristic of a vehicle to adapt the same to the road traffic condition estimated by the aforementioned estimating method and apparatus.
2. Description of the Related Art
A vehicle is equipped with various apparatuses to improve the traveling stability, maneuverability, riding comfort, etc. of the vehicle.
For instance, a vehicle is provided with an electronic fuel supply controller to optimally control the quantity of fuel supplied to an engine in accordance with the vehicle running state represented by a vehicle speed, the opening degree of an accelerator pedal, etc.; an automatic transmission for selecting a gearshift position optimum for the current vehicle running state; and an anti-skid brake system for providing optimum braking power. The vehicle is further equipped with a traction control system for ensuring an optimum slip ratio of driving wheels; a four-wheel steering system for steering rear wheels in the case of turning front-wheels; an active suspension system for variably changing suspension characteristics; and an electric power steering system for variably adjusting the steering power.
The vehicle provided with the aforementioned systems features high maneuverability and running stability, and satisfies, to a great extent, the performance required of a vehicle.
A control method for estimating a traveling state of a vehicle and for controlling various apparatuses so as to be suited to the estimated traveling state (road traffic condition), to thereby permit these apparatuses to fully exhibit their performances has been conventionally known. As parameters from which the traveling state is estimated, a distance between vehicles, a time period elapsed from the moment a vehicle starts to run to the moment the vehicle stops running, a maximum vehicle speed, etc. (see, Japanese Provisional Patent Publication No. 1-119440, for instance).
However, a costly device such as an ultrasonic wave sensor is required to estimate the traveling state (road traffic condition) based on a distance between vehicles. If the estimation on the traveling state is made based on a time period elapsed from the start of vehicle running to the stop of vehicle running, there occurs a small change in an output value even when the vehicle running state changes. Thus, the accuracy of estimation is low. Further, response to a changeover between traveling states, e.g., a changeover from a state where a vehicle travels in a city area to a state where the vehicle travels in an urban district, is poor. Moreover, it is difficult to accurately determine the traveling state based on a maximum speed since the maximum speed varies between individual drivers.